Hydraulic actuator with mechanical feedback

ABSTRACT

A hydraulic actuator having a selectively positioned, rotary output shaft. The actuator includes a control assembly in which a spool valve controls the admission and return of working fluid through a valve port. The spool valve position is controlled by a pilot assembly which communicates with valve chambers exerting pressure on opposite ends of the spool valve. The pilot assembly includes opposed nozzles connected with the valve chambers and a flapper between the nozzles which may be moved back and forth between them to variably restrict their output and hence the pressure in the valve chambers. The flow of fluid from the control assembly is directed to an output assembly which has first and second movable pistons mounted in piston chambers. The first piston chamber is continuously connected to a source of working fluid at supply pressure, while admission of fluid to the second piston chamber is controlled by the spool valve via the valve port. The pistons are connected by a link secured to an output shaft and exert opposing torques on the link. When fluid is directed into the second piston chamber, the second piston exerts the greater torque rotating the shaft in one direction. When fluid is vented from the second piston chamber, the first piston rotates the output shaft in the opposite direction. A finger feeds back a portion of the motion of the link to the flapper via a spring to center the flapper when the output shaft is in a selected position.

United States Patent [19] Cox HYDRAULIC ACTUATOR WITH MECHANICAL FEEDBACK [75] Inventor: Robert M. Cox, Northridge, Calif. [73] Assignee: SL1 Industries, Van Nuys, Calif. [22] Filed: Dpc. 29, 1972 [21] Appl. No: 319,165

Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Abraham Hershkovitz Attorney, Agent, or Firm.-Fulwider Patton Rieber Lee & Utecht [57] ABSTRACT A hydraulic actuator having a selectively positioned,

[ June 18, 1974 rotary output shaft. The actuator includes a control assembly in which a spool valve controls the admission and return of working fluid through a valve port. The spool valve position is controlled by a pilot assembly which communicates with valve chambers exerting pressure on opposite ends of the spool valve. The pilot assembly includes opposed nozzles connected with the valve chambers and a flapper between the nozzles which may be moved back and forth between them to variably restrict their output and hence the pressure in the valve chambers. The flow of fluid from the control assembly is directed to an output assembly which has first and second movable pistons mounted in piston chambers. The first piston chamber is continuously connected to a source of working fluid at supply pressure, while admission of fluid to the second piston chamber is controlled by the spool valve via the valve port. The pistons are connected by a link secured to an output shaft and exert opposing torques on the link. When fluid is directed into the second piston chamber, the second piston exerts the greater torque rotating the shaft in one direction. When fluid is vented from the second piston chamber, the first piston rotates the output shaft in the opposite direction. A finger feeds back a portion of the motion of the link to the flapper via a spring to center the flapper when the output shaft is in a selected position.

11 Claims, 7 Drawing Figures PATENTEDJun 18 m4 SHEEI 1 BF 3 PATENTEBJUIHBIHM v 3 817150 smears PATENTEDJuu 1a 1924 3.811150 SHEEIB 0F 3 HYDRAULIC ACTUATOR WITH MECHANICAL FEEDBACK BACKGROUND OF THE INVENTION This invention relates to a hydraulic actuator having a rotary output shaft in which the position of the output shaft is detected and fed back to a positioning mechanism within the actuator. More particularly, the actuator includes an output assembly in which a shaft is turned by the action of two pistons acting through a linkage; a control assembly by which working fluid is selectively directed to the output assembly through the use of a spool valve; and a pilot assembly to direct the positioning of the spool valve.

Hydraulic actuators of the rotary shaft output type, are widely used in diverse industrial applications e.g., one application would be for controlling the position of a butterfly valve in a flow line. The hydraulic actuator itself may be controlled from a remote location by an operator who can apply an electrical or other signal remotely to the actuator to direct the necessary degree of shaft rotation to accomplish the desired result in the controlled device. Such units often include an output assembly comprising the working parts to which hydraulic fluid is applied and a control assembly which directs the delivery of the working fluid in the appropriate direction and rate to operate the output assembly.

One prior control assembly, disclosed in applicants prior US. Pat. No. 3,698,437 issued Oct. 17, 1972, is intended to control the operation of a linear hydraulic motor comprising a double acting piston mounted in a cylinder. Flow of actuating fluid to and from the hydraulic cylinder is controlled by a spool valve movable within a spool valve housing in opposite directions from a neutral position, in response to a difference in pressures in chambers positioned adjacent the ends of the spool. A pilot valve assembly, mounted on the end of the spool valve housing, includes an electromagnetically actuated flapper for variably restricting flows from the end chambers. Two balanced springs engage opposite sides of the flapper to urge it toward a centered position. A longitudinally slidable feedback pin between one spring and the end of the spool valve adjusts the force of the spring in accordance with changes in the position of the spool.

Although satisfactory for its intended use, certain difficulties may be encountered with a valve of the prior type described. For example, during manufacture, it is necessary to insure that the various fluid directing surfaces on the exterior of the spool valve are machined with a very high degree of precision to insure that as one side of the hydraulic cylinder is connected to the fluid supply, the other side is simultaneously connected to exhaust and vice versa. Manufacturing difficulties inherent in maintaining precise dimensioning can lead to high scrappage rates and increased costs, and it would therefore be desirable to find a construction less demanding in its manufacture.

In addition the prior device, as described, derived the feedback motion to recenter the flapper from the motion of the spool controlling the delivery of fluid to the hydraulic motor rather than directly from the position of the controlled member i.e., the piston rod. However as it is the position of the controlled member that is of ultimate interest it would be preferable to sense the position of that directly for the feedback response, as there is always a possibility of slight variance between the relative motions of the spool and the controlled member due to overshooting, the development of slight play in the spool movement and like causes.

The prior device described is, in addition, disclosed for use with a linear hydraulic motor. There are many applications for which there is a need for an electrohydraulic actuator which has a rotary shaft output. Desirable features of such an actuator are that it should have a high flow rate and a high pressure capability to provide high torque output and rapid operation.

SUMMARY OF THE INVENTION The present invention provides a hydraulic actuator having a rotary shaft output, which is characterized by rapid operation and high torque output. Although the invention utilizes internal components of the spool valve type, the construction is such that the need to maintain high precision tolerances on the spool valve dimensions during manufacture is substantially reduced so that a lower production cost can be achieved. In addition, a hydraulic actuator according to the invention provides a feedback directly responsive to the position of the controlled member.

More particularly, a hydraulic actuator constructed in accordance with the invention includes an output assembly which rotates an output shaft in either direction when actuating fluid is directed to it, a control assembly provided with a movable spool valve for directing the flow of actuating fluid to the output assembly, and a pilot assembly for positioning the spool valve of the control assembly. The control assembly includes a first housing having an internal bore and inlet and outlet passages which admit and exhaust fluid to and from the bore, respectively. A spool valve movably mounted within the bore controls flow of fluid through a valve port. Valve chambers are positioned at opposite ends of the bore and communicate with the inlet passage. The spool valve is acted upon by the difference in pressures within the valve chambers for motion in opposite directions from a neutral position, in which the valve port is closed when the pressures in the valve chambers are equal, to opposite positions in which the valve port communicates with either the inlet passage or the outlet passage dependent upon the direction of the pressure differential between the valve chambers. Flow pas sages communicate with the valve chambers for outflow of fluid therefrom. The pilot assembly includes a second housing, connected with the first, having an internal cavity into which two opposed nozzles open. The nozzles communicate with the flow passages and direct fluid from them into the cavity as opposed jets. A flapper disposed between the nozzles in spaced relation to them is movable back and forth. An electromagnetic actuator, on receipt of an input signal, urges the flapper towards either of the nozzles with a selected variable force. The flapper variably restricts the nozzles and thus varies the pressure in the valve chambers (and hence the position of the spool valve). The output assembly includes a third housing having first and second pistons slidably mounted in corresponding piston chambers. The first piston chamber is in continuous communication with the inlet passage while the second piston chamber communicates with the valve port. Each piston has a piston rod extending outwardly from its associated chamber. The output shaft is rotatably mounted in the third housing and has a link fixed to it which is acted upon by the piston rods to transmit opposing torques to the shaft. When the spool valve connects the valve port to the inlet passage so that both piston chambers are both at the same supply pressure, the torque exerted by the second piston is greater than the torque exerted by the first piston and the link rotates the shaft in one direction. When the spool valve is in the opposite position to vent the second chamber, the torque exerted by the first piston is substantially unopposed and the shaft is turned in the opposite direction. A feedback unit connected with the flapper and the link is responsive to the link movement to urge the flapper to a centered position between the nozzles when the output shaft is in the selected position.

It will be appreciated that this arrangement, in which one of the pistons is continuously connected to the sup ply source, provides a construction in which it is only necessary to control a single valve port to obtain rotary motion in opposite directions. This offers significant manufacturing advantages because it is relatively much less expensive to drill or ream a single valve port to match the dimension between the controlling portions of the spool valve than it is to machine the flow controlling portions-on the exterior of the spool valve with a high degree of precision.

In the preferred embodiment, the desired torque relationship is arranged by utilizing pistons of equal cross sectional area but pivoting the link at a location closer to the first piston rod than to the second piston rod so that the latter exerts the greater torque when both piston chambers are at the same pressure.

The feedback unit includes a finger extending from the link towards the flapper and moved linearly in that direction by pivoting motion of the link. The finger is slidably mounted in the adjacent portions of the housings and has one of its ends contacting the link while its other end contacts a first spring which abuts the flapper. A second spring acting on the other side of the flapper opposes the first spring to urge it to a centered position between the nozzles of the pilot assembly when the spool is in the selected position.

By coupling the motion of the finger to the link, two advantages are attained. Firstly, the feedback response is directly responsive to the position of the controlled member which is the matter of ultimate concern rather than to the position of an intermediate component, the spool valve. The second advantage is that by positioning the point of contact of the finger close to the pivot point, it is possible to obtain a reduction in the linear travel of the finger as compared with the piston travel. Such reduction is necessary because the range of available movement of the flapper between the nozzles is relatively much smaller.

BRIEF DESCRIPTION OF THE DRAWINGS A hydraulic actuator constructed in accordance with the preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a perspective view of a hydraulic actuator constructed in accordance with the preferred embodiment of the invention, shown mounted on an exemplary control device and connected thereto by a parallel arm linkage;

FIG. 2 is a cross-sectional side view of the hydraulic actuator shown in FIG. 1, taken along the lines 2-2 therein;

FIG. 3 is a cross-sectional end view of the hydraulic actuator shown in FIG. 2, taken along the lines 33 therein;

FIG. 4 is a cross-sectional end view of the hydraulic actuator shown in FIG. 2, taken along the lines 4--4 therein, with a spool valve, forming a part of the invention, shown in a neutral position;

FIG. 5 is a cross-sectional end view of a portion of the hydraulic actuator shown in FIG. 2, taken along the lines 5-5 therein;

FIG. 6 is a cross-sectional bottom view of a portion of the hydraulic actuator shown in FIG. 2, taken along the lines 66 therein, but with the spool valve shifted from the neutral position; and

FIG. 7 is a cross-sectional side view of the hydraulic actuator shown in FIG. 6, taken along the lines 7-7 therein.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawings, a hydraulic actuator 2 is there shown, secured to an underlying controlled device 4. The shaft output of the actuator 2 is connected to the input of the controlled device 4 by a connecting parallel arm linkage 6. The controlled device is shown purely for the purposes of exemplification and may be, for example, a valve positioner, a pump controller or any of a very diverse range of devices customarily controlled by a hydraulic actuator having a shaft output.

The hydraulic actuator of the invention, includes three principal assemblies; an output assembly 8 for applying power to turn an output shaft 10 progressively in either direction to any selected position between two extremes of angular movement, a control assembly 12 for controlling the admission and direction of actuating fluid to the output assembly, and a pilot 14 for receiving an electrical positioning signal and actuating the control assembly to deliver fluid to the operating assembly to achieve the desired motion of the output shaft. Actuating fluid under a pressure P is supplied to the control assembly 12 through an inlet connection 16 from a source such as a pump (not shown).

The output assembly 8 (FIGS. 2 and 4) includes a housing 20 provided with spaced, parallel, first and second piston chambers 22 and 24, respectively, of identical configuration. First and second pistons 26 and 28 are sealingly and slidingly received within the first and second chambers and have piston rods of equal length extending outwardly from the chambers in one direction. Actuating fluid, at the supply pressure P, is continuously directed to the first chamber 22 via a vertical inlet passage 30 in a housing 32 (forming a part of the control assembly) and a transverse channel 34 extending between the inlet passage and the first chamber.

Admission of fluid to and from the second chamber 24 is controlled by a spool valve 36 in the control assembly 12, which is movable relative to a valve port 38 (FIG. 6) communicating with the second chamber. In a neutral position of the spool valve 36, it closes the valve port so that the piston remains locked in a stationary position. However, the spool valve may be moved selectively, under the control of the pilot assembly 14, in one direction in which it places the valve port 38 in communication with the inlet passage 30 so that fluid at the supply pressure P is admitted to the second chamber 24, or in an opposite direction in which the valve port 38 communicates with an outlet vent from the hydraulic actuator. When it is in communication with the outlet vent the pressure in the second chamber 24 is reduced to a relatively negligible pressure compared with the supply pressure P.

The first and second pistons 26 and 28 apply torque in opposite directions to the output shaft through a pivoting link 40 (FIG. 2) fixedly secured to the output shaft by a pin 41. The link 40 is provided with bearing units 42 at its opposite ends abutting the free extremities of the piston rods. The shaft 10 is mounted in bearings 44 (FIG. 3) supported by a cover portion 46 of the output assembly 8, at a location closer to the first piston 26 than to the second piston 28. Because the point of pivotal connection of the link (which is the same as the axis of rotation of the output shaft 10) is closer to the first piston, the second piston has greater leverage about the pivot point than the first piston. When the spool valve is moved to put the valve port 38 in communication with the inlet passage thereby causing the supply pressure P to be equally applied to both piston chambers, the second piston 28 exerts a greater torque on the output shaft 10 than the opposite torque exerted by the first piston 26, because of the off-center pivotal connection of the link. The resultant torque causes the output shaft to be rotated in an anticlockwise direction as shown in FIG. 2. However, when the spool valve is shifted in the opposite direction to place the valve port 38 in communication with the outlet vent so that the pressure in the second chamber drops to a relatively negligible value, then the torque exerted by the first piston 26 is substantially unopposed and the link is rotated in a clockwise direction.

It will be appreciated that it is the leverage provided by the pivotal link 40 that enables the system to be operated by control of the fluid supply to only one of the two working pistons so that, while the other exerts a constant torque, the controlled piston can exert either a greater opposite torque using the same supply pressure to rotate the shaft in one direction or a zero torque permitting the shaft to be rotated in the opposite direction. The portions of the link extending on opposite sides from the pivot point to the two pistons constitute two connected crank arms. This ability to operate by control of fluid admission to only one of the working pistons considerably simplifies the spool value structure (to be described hereinafter) leading to considerable manufacturing savings.

This torque relation could also be achieved in whole or part by utilizing pistons of different cross-sectional area in the first and second chambers. For example it would be possible to utilize a link pivoted at its mid point and a second piston twice the area of the first piston to achieve a comparable result.

Because the pistons are of relatively large crosssectional area, a hydraulic actuator in which the resultant output torque is high, is provided. Also, the large flows of actuating fluid that occur in and out of the large piston chambers 22 and 24 provide for particularly rapid response of the device in achieving the desired positional output of the drive shaft 10.

Fluid flow to and from the second chamber 24 is, as previously mentioned, regulated by the spool valve 36 (FIGS. 6 and 7). The spool valve 36 is movably mounted within an enclosed horizontal bore 50 extending transversely within the lower part of the housing 32 of the control assembly. The valve port 38 intersects the bore 50 at approximately its mid point and extends horizontally through the housing 32 to communicate with the second chamber. The spool valve 36 includes a hollow cylindrical valve body 52 spaced concentrically within the bore and of shorter length than the bore. It is provided with axially spaced, first and second annular lands 54 and 56, respectively, which extend into sliding sealing contact with the walls of the bore 50. When the spool valve 36 is in a neutral position, the outer edges of the lands 54 and 56 closely overlap the outer edges of the valve port 38 to close the valve port from fluid communication with the interior of the bore 50 outside the lands (FIG. 4). However, it takes only a slight axial shift of the spool valve to open the valve port 38 for flow of fluid between the second chamber 24 and the bore 50 (FIGS. 6 and 7). This arrangement has a particularly significant advantage from the viewpoint of manufacturing construction. Because only one valve port for the passage of actuating fluid is controlled, the only manufacturing alignment that is needed is to ream the valve port 38 until its diameter is approximately equal to, but slightly less than, the distance between the outer surfaces of the first and second lands 54 and 56. Precise machining of the axial dimensions of the lands themselves is thus rendered unnecessary, thereby substantially reducing manufacturing costs and losses due to scrappage of defectively machined spool valves.

The spool valve 36 also includes third and fourth lands 58 and 60 adjacent and spaced from the first and second lands 54 and 56. The third and fourth lands 58 and 60 are spaced from the adjacent ends of the spool body 52 and extend annularly about the spool body into sliding sealing contact with the bore 50. Incoming actuating fluid passing down the previously mentioned inlet passage 30, which communicates at its lower end with the bore 50, enters the bore 50 between the second and fourth lands 56 and 60 of the spool valve and fills the annular space between the lands and the spool body. The spool valve 36 may be shifted axially in one direction to partially expose the valve part 38 so that the incoming fluid passes from the inlet passage 30 via the space between the lands 56 and 60 through the valve port 38 into the second chamber 24. The axial spacing between the second and fourth lands 56 and 60 is sufficient to insure that the inlet passage 30 remains in fluid communication with the space between the lands, even in the extreme positions of displacement of the spool valve from the neutral position.

To enable outlfow of the actuating fluid from the bore 50, an outlet or vent passage 62 is also provided in the housing 32 of the control assembly. The vent passage 62 extends vertically in spaced parallel relation to the inlet passage 30, but on an opposite side of the valve port 38 from the inlet passage. Adjacent its upper end, which is blocked, the vent passage 62 communicates with an outlet connection 64 to return the actuatin'g fluid to a suitable reservoir (not shown). The pressure of the fluid in the vent passage is substantially lower than the pressure P at which the actuating fluid is supplied and may, for the purposes of description, be regarded as at negligible pressure. The lower end of the vent passage 62 communicates with the bore 50 in the region between the first and third lands 54 and 58 on the spool valve, so that when the spool valve is shifted in an opposite axial direction from its neutral position, the valve port 38 is placed in communication with the vent passage 62 and fluid within the second chamber 24 can escape therefrom as illustrated in FIG. 6. The axial spacing between the lands 54 and 58 is sufficient to insure that the vent passage 62 communicates with the space between the lands, even in the extreme positions of displacement of the spool valve 36.

Shifting of the spool valve axially in the bore is accomplished by exerting differential pressure on its end portions. The end regions of the bore 50, between its right end and the fourth land 60 of the spool valve and between the left end of the bore and the third land 58, constitute first and second valve chambers 66 and 68, respectively. Centering springs 70 between the ends of the bore 50 and the adjacent lands 58 and 60 center the spool in the neutral position in which the valve port 38 is closed when the pressures in the first and second chambers 66 and 68 are equal. Suitable adjustment members (not shown) are provided for adjusting the spring pressures to center the spool during calibration. The actuating fluid at inlet pressure P is admitted to the first and second chambers 66 and 68 via the hollow interior of the spool body 36, through two openings 72 in the spool body in the region between the second and fourth lands 56 and 60. A fixed barrier 74, positioned within the interior of the spool body 52, prevents direct fluid communication between the first and second valve chambers 66 and 68. To permit controlled outflow of fluid from the first and second valve chambers 66 and 68, they are provided with first and second flow passages 76 and 78, respectively, (FIG. 6). If flow out of one of the valve chambers is restricted to a greater extent than flow out of the other, the pressure in the one valve chamber will become relatively higher than in the other. As a result the spool valve will move in the direction of the reduced pressure chamber. Thus, positional control of the spool valve, and hence control of the operation of the output assembly, is effected by varying the rate at which fluid is permitted to escape from the first and second valve chambers 66 and 68, respectively.

The differential control of the outflow of fluid from the valve chambers of the control valve assembly is effected by the pilot assembly 14, which is of substantially the same construction as the corresponding pilot assembly shown in applicants aforementioned US. Pat. No. 3,698,437. The pilot assembly includes a third housing 80 (FIGS. 2 and 6) having a vertical cavity 82 therein and two fixed horizontal nozzles 84 and 86 extending in spaced, opposed, aligned relation into the cavity 82. Between the second and third housings 32 and 80, which are fixedly connected together, there is interposed a plate 88 (FIG. having cut-out openings in which are mounted O-rings to define channels for the passage of fluid. The plate 88 provides a first channel 90 (FIG. 6) which connects the flow passage 78 from the second valve chamber with a chamber 91 communicating with the nozzle 84. The flow passage 76 from the first chamber communicates with a vertical channel 92 in the plate 88, which, at its upper end, communicates with an inclined passage 94 (FIG. 2) extending downwardly into a chamber 95 communicating with the other nozzles 86. Thus, flows of actuating fluid from the two valve chambers 66 and 68 are directed into the cavity 82 as opposed fluid jets. A drain passage 96 (FIG. 2) from the lower end of the cavity 82 returns fluid to a lower end portion of the previously mentioned vent passage 62 extending below the bore 50 (FIG. 7).

Disposed between the two nozzles 84 and 86 is a socalled flapper 98 (FIGS. 2 and 6) which has oppositely facing flat sides adjacent, but spaced from, both nozzles when the flapper is centered. The flapper is movably mounted for swinging of each flat side toward the adjacent nozzle, thereby progressively increasing the restriction of the flow through that nozzle, while simultaneously reducing the restriction of the flow through the other nozzle. As a result, the back pressure in the one of the valve chambers 66 and 68 connected to the restricted nozzle is increased, while the pressure of the other chamber is reduced, thereby unbalancing the forces of the spool valve 36 to cause it to move away from the increased-pressure chamber and toward the reduced-pressure chamber.

The flapper 98 is the flattened lower end of an elongated rod 99 supported adjacent its upper end by a titting 100 which provides for pivoting movement of the rod. The upper end of the flapper rod extends into a electromagnetic torque motor 104 which may be electrically controlled to apply a predeterminedforce to the flapper rod, which is made of a metal subject to magnetic attraction, so that the rod is pivoted on the fitting 100 to cause the flapper rod to move adjacent one or other of the nozzles 84 and 86 with a selected variable force dependent on the magnitude and direction of the electrical input signal. Inasmuch as a complete description of the fitting and the torque motor are provided in applicants prior U.S. Pat. No. 3,698,437, such description is incorporated herein by reference.

Thus, an electrical signal to the torque motor moving the flapper towards one of the nozzles will cause a shift in the position of the spool valve from its centered position and the admission or exhaust of fluid from the second piston chamber, so that the link 40 will be rotated turning the output shaft 10. To cause the rotation to be terminated once the desired angular position has been reached, a feedback mechanism is incorporated into the actuator. For this purpose a feedback finger (FIG. 2), responsive to the movement of the link 40, is provided. The feedback finger includes a pin 112 extending through the housings of the control assembly and the output assembly, and a second pin 114 slidably mounted in the housing of the pilot assembly. The pin 112 has one end in contact with a notch 116 in the mid point of the link 40 and its other end in contact with the pin 114. Both pins are moved linearly towards the flapper rod as the link 40 pivots in a clockwise direction. A spring 118 is compressed between the second pin 114 and the flapper in response to movement of the pin by the link. A similar spring 120 acts against the opposite side of the flapper to counterbalance the force of the first spring 118 thereby holding the flapper centered between the nozzles 84 and 86 when the spool is in the neutral position. The detailed mounting structure of the second pin 114, the springs 120 and 118, and of structure for adjusting the centered position of the flapper rod between the springs is described fully in applicants previously mentioned US. Pat. No. 3,698,437, and such description is incorporated herein by reference.

In operation, when an electrical signal is applied to the torque motor to apply a selected force to the flapper rod to move the flapper towards the nozzle 84, flow out of the second chamber 68 is restricted and the pressure in the chamber 68 is relatively increased, so that the spool shifts connecting the second chamber 24 to the ventpassage as shown in FIG. 6. The-first piston 26 then moves outwardly, rotating the link 40, and the output shaft 10, in clockwise direction as shown in FIG. 2. The motion of the link 40 causes the finger 110 to move toward the flapper rod compressing the spring 118 and exerting a centering force on the flapper rod in Opposition to the signal force, to urge the flapper to a centered position between the nozzles when the output shaft reaches the selected position. As the flapper reaches the centerd position, it causes the spool to move to its neutral position, so that flow to and from the second chamber 24 is shut off and the shaft remains locked in the selected position.

When the electrical input signal moves the flapper towards the other nozzle 86, the spool is moved in the opposite direction to admit actuating fluid into the pressure chamber 24 to cause the piston 28 to rotate the link 40 in an anticlockwise direction. The finger 110 then moves away from the flapper rod reducing the degree of compression of the spring 118 so that the counterforce exerted by the other spring 120 urges the flapper rod back to the centered position.

A further advantage of the link structure described is that by mounting the feedback finger so that it contacts the link adjacent its mid point, the effective length of stroke of the feedback finger is reduced relative to the extent of travel of the pistons. Such reduction in stroke simplifies construction because the range of movement available to the flapper rod between the nozzle is much less than the range of travel through which the piston is moved.

The space within the interior of the cover 46 of the output assembly housing constitutes a fluid filled sump into which leakage of fluid past the pistons drains. The leakage fluid can escape from the sump to the vent passage 62 along an annular channel 122 (FIG. 2) surrounding the finger 112, an opening 124 in the plate 88 and. a connecting duct 126 intersecting the vent passage. Suitable grooves are provided in an enlarged head of. the pin 112 to permit fluid to bypass the enlargement.

Summarizing, a hydraulic actuator according to the present invention possesses high output torque capability by virtue of the large working surfaces of the pistons, and is capable of rapid action due to the large flow of working fluid controlled by the motion of the spool valve which is moved between its flow controlling positions by relatively insignificant control flows of the fluid. The arrangement by which one piston remains permanently, subjected to the full working pressure, while the other piston is provided with a linkage permitting it to exert a greater or less torque than the first piston utilizing the same source of pressure fluid, allows a valving structure wherein only one valve port to the working pistonsneeds to be controlled. As a result, the valve and port structure is considerably simplified and the need for precision machining of the external projecting surfaces of the spool valveis avoided.

A further advantage of the linkage described is the manner in which it enables the stroke of the feedback finger to be reduced to conform with the limited range of flapper movement available, without requiring complicated reduction mechanisms.

It will be apparent to those skilled in'the art that although a particular form of the invention has been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention.

I claim:

1. A hydraulic actuator comprising, a control assem bly having, a first housing, an enclosed bore within said first housing, a valve port communicating with said bore, inlet means adapted for connection to a source of fluid under pressure for admitting fluid under pressure to said bore, outlet means for outflow of fluid from said bore, two valve chambers at opposite ends of said bore in communication with said inlet means, valve means subjected to the pressures within said valve chambers movably mounted within said bore for controlling communication between said valve port and said inlet and outlet means, said valve means occupying a neutral position within said bore in which said valve port is closed when the pressures in said valve chambers are equal, unequal pressures in said valve chambers moving said valve means in opposite directions from said neutral position to positions in which said valve port communicates with one at a time of said inlet means and said outlet means; and two flow passages, each communicating with one of said chambers,

a pilot assembly having a second housing, a cavity in said second housing, opposed nozzles opening into said cavity and communicating with said flow passages to direct fluid therefrom into said cavity as opposed jets, a flapper disposed between said nozzles in spaced relation therewith and movable back and forth between them to variably restrict said nozzles and thereby vary the pressures in said valve chambers, and actuating means for urging said flapper towards either said nozzle with a selected variable force,

an output assembly having a third housing, first and second piston chambers in said third housing, said first piston chamber communicating with said inlet means, said second piston chamber communicating with said valve port, first and second pistons slidably mounted in said piston chambers, each said piston having a piston rod extending outwardly from the associated said piston chamber, an output shaft rotatably mounted in said third housing, a link fixedly secured to said output shaft, the ends of said link acted upon by said piston rods to transmit opposing torques to said output shaft, the torque exerted by said second piston exceeding the torque exerted by said first piston when both piston chambers communicate with said inlet means thereby causing rotation of said output shaft in one direction, the torque exerted by said first piston exceeding the torque exerted by said second piston when said second chamber communicates with said outlet means thereby causing rotation of said shaft in an opposite direction; and

feedback means connected with said flapper and with said link responsive to movement thereof for urging the flapper to a centered position between said nozzles when said output shaft is in a selected position.

2. A hydraulic actuator as defined in claim 1 wherein said feedback means includes,

a finger slidably mounted in the adjacent portions of said housing, one end of said finger contacting said link and moved thereby in a linear direction toward and away from said flapper by pivoting motion of said link, a first spring disposed between one side of said flapper and the opposite end of said finger, said first spring holding said finger against said link, and a second spring acting against the other side of said flapper and opposing said first spring to urge said flapper to a centered position between said nozzles when said output shaft is in said selected position.

3. A hydraulic actuator as defined in claim 1 wherein said first and second pistons are of equal crosssectional area and wherein the axis of rotation of said output shaft is closer to said first piston rod than to said second piston rod to provide sufficient leverage to said second piston to enable it to exert a greater torque on said output shaft than said first piston when both said piston chambers are connected to said inlet means.

4. A hydraulic actuator as defined in claim 1 wherein said bore is of generally cylindrical configuration and said valve means is a spool valve mounted for reciprocation within said bore, said spool valve including a generally cylindrical body concentric with and spaced from said bore, axially spaced, peripherally extending first and second lands fixedly connected with said spool body in sliding sealing contact with said bore; said lands, when said spool is in the neutral position, closely overlapping the opposite edges of said valve port on opposite sides thereof and preventing flow of fluid through said valve port; displacement of said spool from the neutral position in either direction opening said valve port for flow of fluid between the valve port and the interior of said bore.

5. A hydraulic actuator as defined in claim 4 further including,

third and fourth lands spaced on opposite sides of said first and second lands, respectively, said third and fourth lands secured to said spool body extending into sliding sealing contact with said bore, said third and fourth lands being acted upon by the fluid pressures in said chambers to cause axial motion of said spool valve when the pressures are unequal.

6. A hydraulic actuator as defined in claim 1 wherein said valve means further includes,

means for preventing fluid communication between said outlet means and saidfirst and second valve chambers.

7. A hydraulic actuator as defined in claim 2 further including, a fluid filled sump in said third housing enclosing said link, an annular opening extending between said finger and the adjacent portions of said housings through which fluid may pass from said sump, and a passage connecting an outlet end of said annular opening with said outlet means.

8. A hydraulic actuator as defined in claim 3 wherein said feedback means includes.

a finger slidably mounted in the adjacent portions of said housings, one end of said finger contacting said link and moved thereby in a linear direction toward and away from said flapper by pivoting motion of said link, a first spring disposed between one side of said flapper and the opposite end of said finger and holding said finger against said link, and a second spring acting against the other side of said flapper and opposing said first, spring to urge said flapper to a centered position between said nozzles when said output shaft is in a selected position, the point of contact of said finger with said link being intermediate said output shaft and said second piston rod whereby the linear stroke of said finger is less than the linear displacement of said second piston. 9. A hydraulic actuator as defined in claim 5 wherein said inlet means communicates with said bore in a region thereof between said second and forth lands on said spool valve and wherein said outlet means communicates with said bore in a region thereof between said first and third lands on said spool valve, said spool body further including passage means through said spool body and internally thereof for conducting fluid from said inlet means to said first and second valve chambers.

10. In a hydraulic actuator having a pilot valve assembly including a flapper, two orifices for directing jets of hydraulic fluid toward opposite sides of said flapper, actuating means for selectively urging the flapper toward each of the orifices to variably restrict the jet flow therefrom, and feedback means for acting on said flapper in opposition to said actuating means in accordance with the response of a controlled device, and including a movable feedback element; and a control assembly having an inlet for actuating fluid, on outlet for said actuating fluid, and a valve port, valve means movable back and forth along a predetermined path within the control assembly for selectively connecting and disconnecting said valve port with one at a time, or neither, of said inlet and said outlet indifferent positions along said path, and two pressure chambers for applying actuating pressure to said valve means to variably position the latter along said path, the improvement comprising:

an output assembly having a rotary output member, first and second crank arms on said output member for turning the latter, first and second hydraulic cylinders having actuating elements engaging said first and second crank arms, respectively, to apply opposed actuating torques to said output member and also having first and second actuating chambers for said actuating elements, said second chamber communicating with said valve port, means for delivering fluid under a preselected pressure to said first chamber to apply torque to said output member through said crank arm that is less than the torque applied through said second crank arm when said inlet is connected to said valve port;

and a feedback connector acting between said feedback element and one of said crank arms at a point spaced from said output member to transmit rotary motion of said output member to said feedback element.

11. A hydraulic actuator comprising, an output assembly having a first housing, first and second piston chambers in said first housing, said first piston chamber adapted for continuous connection to a source of fluid at a supply pressure, first and second pistons slidably mounted in said piston chambers, an output shaft rotatably mounted in said first housing, crank arms connected with said output shaft and said pistons to transmit opposing torques to said output shaft, the torque exerted by said second piston exceeding the torque exerted by said first piston when both piston chambers are at the same pressure thereby causing rotation of said output shaft in one direction, the torque exerted by said first piston exceeding the torque exerted by said second piston when said second chamber is at a return pressure lower than the supply pressure thereby causing rotation of said shaft in an opposite direction;

a control assembly having a second housing provided with an inlet for incoming flow fluid at the supply pressure, an outlet for exit of fluid at the return pressure and a port communicating with said second piston chamber; and valve means movable relative to said second housing for closing said port and for selectively placing said port in communication with either of said inlet and said outlet,

pilot assembly having a third housing and a movable member resiliently biased in two opposite directions toward a neutral position, signal controlled means for exerting a force of predetermined magnitude on said movable member to displace it in either of said two directions on application of a signal to said signal controlled means, means responsive to the position of said movable member connected with said valve means for causing movement thereof, said responsive means causing said valve means to close said port when said movable member is in the neutral position and causing said valve means to place said second piston chamber in communication with either of said inlet and outlet when said movable member is displaced in the opposite directions; and

feedback means connected with at least one of said crank arms and with said movable member for urging the latter to said neutral position when said output shaft is in a selected position.

po oso sTz-mss PATENT 01 1 11211 (5/69) 1,. a r Ciiufi'lll'm NATE 0F (WERE, "TLQN Patent No. 3, 817,150 Dated June 18. 1974 Inventor(s) ROBERT M. cox

It is certified that error appeazs in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01. .5, line :16, "value" should be -va1ve---.

Col. 9 line 10 "centerd should be --ce'nter ed- 001, 11', line 54, should. be 1 Col I2 line 22 "on" shcjuld be an- Signed and sealed this 12th. day of Ndvember 1974.

' V (SEAL) I 1 Attest: I

McCOY 14,, GIBSON JR. 1 i c. MARSHALL DANDY Attestlng Officer 3 t. 1 'Cdrmnis sion j; .of. Patents 

1. A hydraulic actuator comprising, a control assembly having, a first housing, an enclosed bore within said first housing, a valve port communicating with said bore, inlet means adapted for connection to a source of fluid under pressure for admitting fluid under pressure to said bore, outlet means for outflow of fluid from said bore, two valve chambers at opposite ends of said bore in communication with said inlet means, valve means subjected to the pressures within said valve chambers movably mounted within said bore for controlling communication between said valve port and said inlet and outlet means, said valve means occupying a neutral position within said bore in which said valve port is closed when the pressures in said valve chambers are equal, unequal pressures in said valve chambers moving said valve means in opposite directions from said neutral position to positions in which said valve port communicates with one at a time of said inlet means and said outlet means; and two flow passages, each communicating with one of said chambers, a pilot assembly having a second housing, a cavity in said second housing, opposed nozzles opening into said cavity and communicating with said flow passages to direct fluid therefrom into said cavity as opposed jets, a flapper disposed between said nozzles in spaced relation therewith and movable back and forth between them to variably restrict said nozzles and thereby vary the pressures in said valve chambers, and actuating means for urging said flapper towards either said nozzle with a selected variable force, an output assembly having a third housing, first and second piston chambers in said third housing, said first piston chamber communicating with said inlet means, said second piston chamber communicating with said valve port, first and second pistons slidably mounted in said piston chambers, each said piston having a piston rod extending outwardly from the associated said piston chamber, an output shaft rotatably mounted in said third housing, a link fixedly secured to said output shaft, the ends of said link acted upon by said piston rods to transmit opposing torques to said output shaft, the torque exerted by said second piston exceeding the torque exerted by said first piston when both piston chambers communicate with said inlet means thereby causing rotation of said output shaft in one direction, the torque exerted by said first piston eXceeding the torque exerted by said second piston when said second chamber communicates with said outlet means thereby causing rotation of said shaft in an opposite direction; and feedback means connected with said flapper and with said link responsive to movement thereof for urging the flapper to a centered position between said nozzles when said output shaft is in a selected position.
 2. A hydraulic actuator as defined in claim 1 wherein said feedback means includes, a finger slidably mounted in the adjacent portions of said housing, one end of said finger contacting said link and moved thereby in a linear direction toward and away from said flapper by pivoting motion of said link, a first spring disposed between one side of said flapper and the opposite end of said finger, said first spring holding said finger against said link, and a second spring acting against the other side of said flapper and opposing said first spring to urge said flapper to a centered position between said nozzles when said output shaft is in said selected position.
 3. A hydraulic actuator as defined in claim 1 wherein said first and second pistons are of equal cross-sectional area and wherein the axis of rotation of said output shaft is closer to said first piston rod than to said second piston rod to provide sufficient leverage to said second piston to enable it to exert a greater torque on said output shaft than said first piston when both said piston chambers are connected to said inlet means.
 4. A hydraulic actuator as defined in claim 1 wherein said bore is of generally cylindrical configuration and said valve means is a spool valve mounted for reciprocation within said bore, said spool valve including a generally cylindrical body concentric with and spaced from said bore, axially spaced, peripherally extending first and second lands fixedly connected with said spool body in sliding sealing contact with said bore; said lands, when said spool is in the neutral position, closely overlapping the opposite edges of said valve port on opposite sides thereof and preventing flow of fluid through said valve port; displacement of said spool from the neutral position in either direction opening said valve port for flow of fluid between the valve port and the interior of said bore.
 5. A hydraulic actuator as defined in claim 4 further including, third and fourth lands spaced on opposite sides of said first and second lands, respectively, said third and fourth lands secured to said spool body extending into sliding sealing contact with said bore, said third and fourth lands being acted upon by the fluid pressures in said chambers to cause axial motion of said spool valve when the pressures are unequal.
 6. A hydraulic actuator as defined in claim 1 wherein said valve means further includes, means for preventing fluid communication between said outlet means and said first and second valve chambers.
 7. A hydraulic actuator as defined in claim 2 further including, a fluid filled sump in said third housing enclosing said link, an annular opening extending between said finger and the adjacent portions of said housings through which fluid may pass from said sump, and a passage connecting an outlet end of said annular opening with said outlet means.
 8. A hydraulic actuator as defined in claim 3 wherein said feedback means includes. a finger slidably mounted in the adjacent portions of said housings, one end of said finger contacting said link and moved thereby in a linear direction toward and away from said flapper by pivoting motion of said link, a first spring disposed between one side of said flapper and the opposite end of said finger and holding said finger against said link, and a second spring acting against the other side of said flapper and opposing said first spring to urge said flapper to a centered position between said nozzles when said output shaft is in a selected position, the point of contact of said finger with said link being intermediate saiD output shaft and said second piston rod whereby the linear stroke of said finger is less than the linear displacement of said second piston.
 9. A hydraulic actuator as defined in claim 5 wherein said inlet means communicates with said bore in a region thereof between said second and forth lands on said spool valve and wherein said outlet means communicates with said bore in a region thereof between said first and third lands on said spool valve, said spool body further including passage means through said spool body and internally thereof for conducting fluid from said inlet means to said first and second valve chambers.
 10. In a hydraulic actuator having a pilot valve assembly including a flapper, two orifices for directing jets of hydraulic fluid toward opposite sides of said flapper, actuating means for selectively urging the flapper toward each of the orifices to variably restrict the jet flow therefrom, and feedback means for acting on said flapper in opposition to said actuating means in accordance with the response of a controlled device, and including a movable feedback element; and a control assembly having an inlet for actuating fluid, on outlet for said actuating fluid, and a valve port, valve means movable back and forth along a predetermined path within the control assembly for selectively connecting and disconnecting said valve port with one at a time, or neither, of said inlet and said outlet in different positions along said path, and two pressure chambers for applying actuating pressure to said valve means to variably position the latter along said path, the improvement comprising: an output assembly having a rotary output member, first and second crank arms on said output member for turning the latter, first and second hydraulic cylinders having actuating elements engaging said first and second crank arms, respectively, to apply opposed actuating torques to said output member and also having first and second actuating chambers for said actuating elements, said second chamber communicating with said valve port, means for delivering fluid under a preselected pressure to said first chamber to apply torque to said output member through said crank arm that is less than the torque applied through said second crank arm when said inlet is connected to said valve port; and a feedback connector acting between said feedback element and one of said crank arms at a point spaced from said output member to transmit rotary motion of said output member to said feedback element.
 11. A hydraulic actuator comprising, an output assembly having a first housing, first and second piston chambers in said first housing, said first piston chamber adapted for continuous connection to a source of fluid at a supply pressure, first and second pistons slidably mounted in said piston chambers, an output shaft rotatably mounted in said first housing, crank arms connected with said output shaft and said pistons to transmit opposing torques to said output shaft, the torque exerted by said second piston exceeding the torque exerted by said first piston when both piston chambers are at the same pressure thereby causing rotation of said output shaft in one direction, the torque exerted by said first piston exceeding the torque exerted by said second piston when said second chamber is at a return pressure lower than the supply pressure thereby causing rotation of said shaft in an opposite direction; a control assembly having a second housing provided with an inlet for incoming flow fluid at the supply pressure, an outlet for exit of fluid at the return pressure and a port communicating with said second piston chamber; and valve means movable relative to said second housing for closing said port and for selectively placing said port in communication with either of said inlet and said outlet, a pilot assembly having a third housing and a movable member resiliently biased in two opposite directions toward a neutral position, signal controlled means for eXerting a force of predetermined magnitude on said movable member to displace it in either of said two directions on application of a signal to said signal controlled means, means responsive to the position of said movable member connected with said valve means for causing movement thereof, said responsive means causing said valve means to close said port when said movable member is in the neutral position and causing said valve means to place said second piston chamber in communication with either of said inlet and outlet when said movable member is displaced in the opposite directions; and feedback means connected with at least one of said crank arms and with said movable member for urging the latter to said neutral position when said output shaft is in a selected position. 